Baths for the production of copper electroplates



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Unite lice 3,051,634 RATES FOR THE PRODUCTHGN OF COPPER ELECTROPLATES Wennemar Straus and Wolf-Dieter Willmund, Dusseldorf-Holthausen, Germany, assignors to Dehydag, Deutsche Hydrierwerke G.m.b.H., Dusseldorf, Germany, a corporation of Germany No Drawing. Filed Nov. 21, 1958, Ser. No. 775,354 Claims priority, application Germany Nov. 30, 1957 10 Claims. (Cl. 204-52) This invention relates to a process for producing bright copper electrodeposits from acid copper plating baths using organic compounds as brightening additives. It more specifically relates to supplementary additives for such copper plating baths to permit operation of the bath over wider ranges of temperature and current density without reducing the effectiveness of the bath and the quality of the electrodeposits.

It is known that organic brighteners may be added to copper electroplating baths to achieve bright copper electrodeposits. These brighteners produce a substantial improvement in the brighteners, depending upon their nature, but in many cases their effectiveness is strongly dependent upon temperature, i.e., they can be used effectively only within relatively narrow temperature limits.

It is an object of this invention to provide a method and bath for producing bright copper electrodeposits at higher temperature conditions.

Another object is to provide a method and bath for producing bright copper electrodeposits at lower current density.

A further object of this invention is to provide additives for an acid bright copper electroplating bath which will permit operation of the bath over wider temperature and current density ranges without loss of brightness in the metal deposits.

These and other objects of our invention will become apparent as the description thereof proceeds.

We have now found that this temperature range can be widened by adding acyclic or cyclic thioamides or isothioamides to the baths in addition to the brightening agents. The efiect achieved thereby is that the undesirable dull zones which form at higher temperatures in the range of low current densities of about -4 amp./dm. no longer occur.

Suitable brighteners are the known, previously customary agents such as thiourea, thiourea derivatives, safranins or also, with particular advantage, modern highquality bn'ghteners. The latter are characterized by a carbon atom linked only to heteroatoms, the carbon atom being also linked through a sulfur or nitrogen atom to an aliphatic radical which in turn has a water-solubilizing group, such as a sulfonic acid group, attached thereto.

The thioamides or isothioamides which are the subject matter of this invention, have a general structural formula as follows:

Fr R-C-N wherein R, R and R" are aliphatic, cycloaliphatic, alkylaromatic or aromatic hydrocarbon radicals, and R or R" may also be hydrogen. R and R (or R") as well as R and R" may also form a polymethylene chain which may, in the latter case, be interrupted by heteroatoms. The radicals R, R and R may carry substituents, such as halogen, cyano, thiocyano and/ or hydroxyl groups, or may be interrupted by heteroatoms or heteroatom groups; particularly, they may contain additional thioamide groups. Products of this type are soluble in the acid copper baths in the customary concentrations. They may be improved with respect to solubility properties, if necessary, by introducing non-ionic, Water-solubilizing groups, such as polyethylene-oxide groups.

The addition of these compounds permits operation at bath temperatures up to 55 C. and produces from bright to full bright electrodeposits, depending upon the nature of the brightener, over the entire current density range. If desired, two or more of these agents may be used simultaneously. Mixtures of halogen-free and halogen containing thioamides or isothioamides have been found to be particularly advantageous and result in a considerable increase in the eflect.

Examples of thioamides or isothioamides which may be used in accordance with the present invention are:

Thioacetamide Thiopropionamide Thiobutyramide Adipic acid dithioamide Thiobenzamide Z-hydroxy-thiobenzamide Phenyl-thioacetamide Thionaphthamide N,N-diethyl-thioacetamide N,N-diethanol-thioacetamide N-ethyl-thioacetamide Thioacetanilide 'I'hioacet-m-chloroanilide N-cyclohexyl-thioacetamide N- (fifl e-trichloro-a-hydroXy-ethyl) -thioacetarnide Thioacet-morpholide Thioacet-piperidide 1,2-ethylene-bis-(thioacetiminoester-S,S) Thioacetimino-allylester N-methyl-N-B-chloroethyl-thiopropionamide N-methyl-N-q -chloropropyl-thiopropionamide N-methyl-N-fi-chloroethyl-thiobenzamide N-cyclohexyl-thiobutyramide 2-hydroXy-thiobenz-piperidide Butyrothiolactam Valerothiolactam Caprothiolactam N-chloroalkyl-caprothiolactams, such as N-fi-chloroethyl-caprothiolactam N-y-chloropropyl-methyl-valerothiolactam N,N'-bis- (thioacet) -ethylenediamine The addition product of 5 mols of ethylenoxide to thio acetamide.

As already indicated, suitable brighteners are the known previously customary agents such as thiourea derivatives, safranins and the full brightening agents which may be used are primarily those organic compounds which are characterized by one or more carbon atoms linked only to heteroatoms, and which contain a short aliphatic radical linked to the carbon atom through a sulfur or nitrogen atom, the aliphatic radical having attached thereto a water-solubilizing group, especially a sulfonic acid group. Examples of such full brightening agents are water-soluble salts of N,N-diethyl-dithiocarbamic acid-n-propylester-wsulfonic acid; N,N-pentamethylene-dithiocarbamic acid-npropylester-w-SO H; 1,3,S-triazine-2,4,6-tris-(mercapto-2'- hydroXy-propane-sulfonic acid); and other full brightening agents of similar structure, such as those which are described in French Patent No. 1,097,123 and Belgian Patents Nos. 543,413 and 540,564 or which are the subject matter of copending application Serial No. 618,183, filed October 25, 1956, now Patent No. 2,849,352.

Furthermore, the baths may be modified with agents which render bath impurities harmless and which improve the ductility of the electrodeposits. If desired, the baths may contain additional brightening and/ or Wetting agents.

The addition of agents which render bath impurities 3 harmless has the effect that inorganic impurities, such as the hardness components of water or impurities in technical grade metal salts, do not exert a detrimental eflect upon the properties of metal electrodeposits which are produced with the aid of the above full brighteners. Furthermore, these compounds have the property of increasing the ductility of the electrodeposits.

Examples of compounds of this type are:

N,N,N',N'-tctraethyl-1,3-diamino-propanol-2,N,N,N,N-

tetraethanol-ethylenediamine Z-diethylamino-ethylchloride-l N,N,-dimethyl-4-bromaniline 3-diethylamino-1-chloro-propanol-2 as well as halogen salts of quaternary ammonium compounds which have been formed by intramolecular rearrangement from the last-mentioned substances, and piperaZine-N,N'-bis-(2-hydroxypropane-sulfuric acid) N,N,N, N-tetra-n-butyl-1,3-diamino-propanol-2-monosulfuric acid ester and similar compounds, such as those which are described in German Patents 934,508 and 1,000,204, German published specification 1,014,404, and in copending application Serial No. 714,687, now US. Patent No. 2,986,498.

The additives according to the present invention may also be used conjointly with the above-described hardnessbinding and ductility-improving amino compounds free from car-boxyl groups, as well as with the full brighteners in the process for directly copper plating non-precious metals in accordance with copending application Serial No. 458,983, now US. Patent No. 2,903,403. According to that process it is possible to deposit firmly adhering copper electroplates on non-precious metals, such as iron, without a cyanide pre-dip by pre-treating the metal objects to be copper plated in an acid pickling bath in the presence of inhibitors having a high inhibiting effect, and subsequently directly electroplating them in a copper bath without intermediate rinsing.

The additives according to the present invention are employed in amounts of about 0.001 to 6 gm./1iter, preferably in amounts of 0.01 to 1 gm./ liter of bath.

From German Patent 837,029 it is known that thioacetamides may be added to copper electroplating baths in order to improve the brightness of the electrodeposits. However, it was found that only a very moderate brightening eifect could be achieved with these substances alone. In contrast thereto, the present invention concerns the improvement of baths which contain known full brighteners, because the addition of thioamides achieves a substantial widening of the' effective temperature range of the copper electroplating process.

The following examples are set forth to enable persons skilled in the art to better understand and practice the invention. It will be understood that there is no intention of limiting the invention to these examples.

Example 1 Metal objects were electroplated at room temperature in an acid copper bath which contained 200 gm./liter CuSo .5H O, 60 gm./Iiter concentrated H SO 0.2 gm./ liter N,N-diethyl-dithiocarbamic acid-n-propylester-w-sulfonic acid (sodium salt) and 0.4 gm./liter 1,3,5-triazine- 2,4,6-tris-(mercapto-ethane sulfonic acid) (sodium salt) as a brightening agent, 0.25 gn1./liter N,N,N,N'-tetraethyl-ethylenediarnine as a ductility-improving agent, and 3 gm./1iter of a condensation product formed from dodccylalcohol and 10 mols ethyleneoxide, which had been 25% converted into the sulfuric acid ester, as a wetting agent. =Full bright copper electroplates were obtained in a current density range of about -7 amp./dm. However, iftheobjects are electroplated in the same bath at a higher temperature, for example at 35 'C., only dull electroplates were obtained in the range of 0-4 amp./dm. whereas full bright deposits were obtained in the range of 4-8 amp./dm. However, when the bath was modified with 0.002 gm./liter caprothiolactam, the range offull bright deposits was extended to about 0-8 amp./dm. i.e.,

full brightness again occurred over the active current density range.

In place of caprothiolactam, the following thioamides may be used with comparable results: N-fi-chloroethylcaprothiolactam, methyl-valerothiolactam, N,N-bis-(thioacet)-ethylenediamine, thioacetmorpholide, N,N-diethanol-thioacetamide thioacetimino-allylester, N-cyclohexylthioacetamide.

Example II The copper electroplating bath described in Example I was modified in additon with 0.008 gm./liter thioacet-mchloroanilide. Full bright copper electrodeposits were obtained even at 55 C. In this case the eifective current density range was 0.5-8.5 amp./dm.

Example 111 In an acid copper electroplating bath, containing 200 gm./liter CuSO .5H O, 60 gm./ liter concentrated H 30 0.025 gm./ liter of the sodium salt of N,N-dimethyl-dithiocarbamic acid-ethyl ester-w-sulfonic acid, 0.5 gm./liter dimethyl-,B-chloroethyl-amine hydrochloride, 4 gm./liter of a condensation product of dodecyl alcohol and 10 mols ethyleneoxide, which had been completely transformed into the sulfuric acid ester, full bright electrodeposits were obtained at a temperature of 35 C. within a current density range of 0-8 amp./dm. when 0.003 gm./liter phenylthioacetamide was added to the bath.

Corresponding results were obtained if thiobenzanilide, thio-B-naphthamide, 2-hydroxy-thiobenzamide and others were used in place of phenyl-thioacetamide.

Example IV To an acid copper bath, containing 200 gm./liter CUSO4-5H2O 60 grn./liter concentrated H 50 and 4 gm./liter of the wetting agent of Example III, 0.1 gm./liter N,N-diethyldithiocarbamic acid-n-propylester-w-sodium sulfonate were added as brightening agents, 2.5 gm./liter of the of 0-7 amp./drn. Example V In place of the brightener, ductility-improving agent acid additive for increasing the temperature range indicated in Example IV, 0.25 gm.,/liter N,Ndiethyl-dithiocarbarnic acid-n-2-hydroxy propyl ester-w-sodium sulfonate, 0.15 gm./1it er 1,3-diamino-propanol-2-sulfuric acid ester and 0.02 gin/liter N-(p,fi, 3-trich1oro-arhydroxyethyl)-thioacetamide were added to the acid copper bath. Full bright copper electrodeposits were obtained in this bath at a temperature of 38 C.

Example VI In an acid copper bath, containing 200 gm./ liter CuSO .5H O

60 gm./liter concentrated H 4 gm./liter of the wetting agent used in Example III, and 0.02 gm./liter N,N-diethyldithiocarbamic acid-ethyl ester-w-sodium sulfonate, full bright electrodeposits were obtained up to a temperature of 28 C. Where 0.01 gm./liter thioacetamide are added to this bath, it was possible to obtain full bright copper electrodeposits even at a temperature of 37 C.

While we have disclosed certain specific embodiments of our invention, we wish it to be understood that these are not intended to be limitative, and that various changes and modifications may be made without departing from the spirit of our invention or the scope of the appended claims.

We claim:

1. An acid copper electroplating bath for producing bright copper deposits comprising an aqueous acid solution of a copper salt, an organic sulfonic acid full brightening agent having at least one carbon atom linked only to heteroatoms and a short aliphatic radical linked to the said carbon atom through a member of the group consisting of a nitrogen atom and a sulfur atom, the aliphatic radical having attached thereto a sulfonic acid group, and a compound in sufiicient amount to broaden the effective operating ranges of current density and temperature, said compound being selected from the group consisting of thiocarboxylic acid amides and isothiocarboxylic acid amides.

2. An acid copper electroplating bath for producing bright copper deposits comprising an aqueous acid solution of a copper salt, an organic sulfonic acid full brightening agent having at least one carbon atom linked only to herteoatoms and a short aliphatic radical linked to the said carbon atom through a member of the group consisting of a nitrogen atom and a sulfur atom, the aliphatic radical having attached thereto a sulfonic acid group, and a compound in suflicient amount to broaden the elfective operating ranges of current density and temperature, said compound being selected from the group consisting of thiocarboxylic acid amides and isothiocarboxylic acid amides having the respective formulas wherein R, R and R are radicals selected from the group consisting of hydrogen, aliphatic, cycloaliphatic, alkyl-aromatic and aromatic hydrocarbon radicals and derivatives of the said hydrocarbon radicals.

3. The bath of claim 2, wherein the R radical is a derivative of said hydrocarbon radicals substituted with radicals selected from the group consisting of halogen, cyano, thiocyano and hydroxyl radicals.

4. The bath of claim 2, wherein the R, R and R" radicals contain thiocarboxylic acid amide groups.

5. An acid copper electroplating bath for producing bright copper deposits comprising an aqueous acid solution of a copper salt, an organic brightening agent, comprising a mixture of N,N-diethyl-dithiocarbamic acid-N- propylester-w-sulfonic acid (sodium salt) and 1,3,5-triazine-2,4,6-tris-(mercapto-ethane sulfonic acid) (sodium salt), and as a compound for broadening the effective operating ranges of current density and temperature, thioacet-m-chloroanilide.

6. A method for broadening the efiective operating ranges of temperature and current density in an acid copper electroplating bath containing organic sulfonic acid full brightening agent having at least one carbon atom linked only to heteroatoms and a short aliphatic radical linked to the said carbon atom through a member of the group consisting of a nitrogen atom and a sulfur atom, the aliphatic radical having attached thereto a sulfonic acid group comprising the step of adding to said bath a compound selected from the group consisting of thiocarboxylic acid amides and isothiocarboxylic acid amides.

7. A method for broadening the effective operating ranges of temperature and current density in an acid copper electroplating bath containing organic sulfonic acid full brightening agent having at least one carbon atom linked only to heteroatoms and a short aliphatic radical linked to the said carbon atom through a member of the group consisting of a nitrogen atom and a sulfur atom, the aliphatic radical having attached thereto a sulfonic acid group comprising the step of adding to said bath a compound selected from the group consisting of thiocarboxylic acid amides and isothiocarboxylic acid amides having the respective formulas wherein R, R and R" are radicals selected from the group consisting of hydrogen, aliphatic, cycloaliphatic, alkylaromatic and aromatic hydrocarbon radicals and derivatives of said hydrocarbon radicals.

8. The method of claim 8, wherein the R radical is a derivative of said hydrocarbon radicals substituted with radicals selected from the group consisting of halogen, cyano, thiocyano and hydroxyl radicals.

9. The method of claim 7, wherein the R, R and R" radicals are derivatives of said hydrocarbon radicals which contain thiocarboxylic acid amide groups.

10. A method for broadening the effective operating ranges of temperature and current density in an acid copper electroplating bath containing organic brightening agents comprising a mixture of N,N-diethyldithiocarbamic acid-N-propylester-w-sulfonic acid (sodium salt) and 1,3,5-triazine-2,4,6-tris-(mercapto-ethane sulfonic acid) (sodium salt), comprising the step of adding to said bath thioacet-m-chloroanilide.

References Cited in the file of this patent UNITED STATES PATENTS 2,489,538 Phillips et a1 Nov. 29, 1949 2,663,684 Pierce Dec. 22, 1953 2,773,022 Turner Dec. 4, 1956 2,837,472 Gundel et al June 3, 1958 2,849,351 Gundel et al Aug. 26, 1958 2,849,352 Kirstahler et al Aug. 26, 1958 2,910,413 Strauss et al. Oct. 27, 1959 2,937,978 Strauss et a1 May 24, 1960 

1. AN ACID COPPER ELECTROPLATING BATH FOR PRODUCING BRIGHT COPPER DEPOSITS COMPRISING AN AQUEOUS ACID SOLUTION OF A COPPER SALT, AN ORGANIC SULFORNIC ACID FULL BRIGHTENING AGENT HAVING AT LEAST ONE CARON ATOM LINKED ONLY TO HETEROATOMS AND A SHORT ALIPHATIC RADICAL LINKED TO BE SAID CARBON ATOM THROUGH A MEMBER OF THE GROUP CONSISTING OF A NITROGEN ATOM AND A SULFUR ATOM, THE ALIPHATIC RADICAL HAVING ATTACHED THERETO A SULFONIC ACID GROUP, AND A COMPOUND IN SUFFICIENT AMOUNT TO BROADEN THE EFFECTIVE OPERATING RANGES OF CURRENT DENSITY AND TEMPERATURE, SAID COMPOUND BEING SELECTED FROM THE GROUP CONSISTING OF THIOCARBOXYLIC ACID AMIDES AND ISOTHIOCARBOXYLIC ACID AMIDES. 